Technical Field
The present disclosure relates to a lens assembly. More particularly, the present disclosure relates to a compact lens assembly which is applicable to NIR (Near-Infrared) imaging.
Description of Related Art
In recent years, as portable electronic devices like smartphones become more widespread, the demands for better optics for a wider range of applications (such as better quality photographs, better security features . . . etc.) have also dramatically increased. It has become increasingly difficult to meet the increasing optical quality standards, especially for imaging of electromagnetic radiation with wavelengths in a range of 750 nm to 1100 nm (i.e. NIR radiation), and improvements are often gained at the cost of aesthetics. Also, as the lens assembly gets smaller in size, it becomes more difficult to reduce stray radiation, especially in NIR imaging, wherein both NIR and VIS (Visible) radiation become possible sources of interference with the image, thus novel ways of reducing such interferences are required.
One of the conventional technologies teaches a lens assembly for electromagnetic radiation with wavelengths in a working range of 750 nm to 2000 nm, wherein the technology incorporates a lens element absorbing electromagnetic radiation with wavelengths in a range of 350 nm to 700 nm (i.e. VIS radiation) and allowing NIR radiation to pass. While this improves NIR imaging capabilities of the lens assembly, it is insufficient to optimally keep stray radiation out, for example, some stray radiation can be reflected through the gaps between the lens elements and the housing.
The technology also teaches the lens assembly including a last lens element, which is the lens element closest to the image surface of the lens assembly, and has positive refractive power and a convex image-side surface. This arrangement is unsuited for reducing the overall size of the lens assembly, as the positive refractive power and the convex image-side surface cause a principle point of the lens assembly to be too close to the image surface to reduce the back focal length, which hinders miniaturization.
In addition, the lens assembly including housing itself may not look aesthetically pleasing. Aesthetics is important aspect as the lens element of NIR imaging is often pointed towards the users, thus the lens element of NIR imaging is more visible than the lens element of typical rear facing VIS imaging during normal usage.
Given the above, the conventional lens assemblies of NIR imaging cannot satisfy the requirements of compact size, reducing stray radiation, enhancing image quality and improving aesthetics, so there is an urgent need in developing a lens assembly of NIR imaging with the features of compact size, reducing stray radiation, enhancing image quality and improving aesthetics.